Beamforming is a method for using wireless channel information to transmit signals to the receiver in order to improve reception quality, and increase data throughput in a Multi-In, Multi-Out (MIMO) communication system. This requires that the channel sounding packets be processed at the receiver and the beamforming information be retransmitted back to the transmitter in a closed loop fashion. The remaining issue for closed loop beamforming is system stability. In general, the beamforming parameters are very straightforward to compute for a given channel condition. However, the wireless channel between the transmitter and receiver is constantly changing, due to changes in the environment, which cause fluctuation in the Signal-to-Noise Ration (SNR) and varying multipath conditions. Therefore, a certain set of beamforming parameters may not apply to the current channel, and be considered “stale”. If a closed loop system does not anticipate the changing channel conditions, and does not qualify beamforming sets, the throughput can degrade, and the link can become unstable.
It is unclear how the problem of “channel tracking” is currently solved. Most systems in the literature assume the channel is not changing, and that the beamforming parameters for the particular channel are known at the transmitter. This invention specifically addresses the closed loop beamforming issue of changing channel conditions.
Varying embodiments of the present invention describe a closed loop system for processing the beamforming information, qualifying the expected performance, activating and deactivating the beamforming system. The invention utilizes well-defined metrics to indicate a change in the channel state, and apply a new sounding packet in order to update the beamforming parameters. Using periodic soundings, changing channel conditions are thus automatically detected and compensated. The advantage is that the link stability is improved, and high throughput with active beamforming is maintained.
A first embodiment is a method for closed loop beamforming in a wireless communication system, the system comprising a transmitter and a receiver, the method comprising initiating beamforming on a communication channel between the transmitter and the receiver, monitoring the communication channel, periodically determining a condition of the communication channel and controlling beamforming based on the condition of the communication channel.
A second embodiment is a wireless communication system comprising a transmitter, a receiver, a communication channel for communication there between wherein the transmitter and receiver each include at least one software module capable of performing the following steps initiating beamforming on the communication channel between the transmitter and the receiver, monitoring the communication channel, periodically determining a condition of the communication channel and controlling beamforming based on the condition of the communication channel.
Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.